Instead of looking for a specific file via the file system which would "depend" on systemd in as much as systemd provides the /dev/by-uuid/ directory (AFAIR anyway), maybe look into the blkid.h file included in linux-utils.
libblkid(3), blkid(8) are some good man pages to start out with.
I haven't used blkid.h myself, but given what the blkid command does I think it's fair to say its library may be fruitful for your purposes.
Sure, it's not cross-platform to BSDs and such, but it'll at least get you out of the systemd requirement :)
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Wednesday, April 29, 2020 7:02 PM, lmsrusso_AT_gmail.com <lmsrusso_AT_gmail.com> wrote:
> Hi,
>
> I have just developed a PAM module that can be used to log into linux
> by using a usb drive. The software was designed according to the
> suckless philosophy of simplicity, clarity and frugality. However it
> does depend on systemd, so any suggestion on how to achieve the same
> functionality without this dependency is welcome.
>
> The code is hosted at GitHub
>
> https://github.com/LuisRusso/PamUUID
>
> Besides announcing the software to the community I would like to
> request that it be added in the "other projects" list of the suckless
> webpage.
>
> Best regards,
>
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Luís M. S. Russo
Received on Wed Apr 29 2020 - 23:41:03 CEST